湖相叠层石纹层的碳氧同位素特征及其生长节律的古环境意义  

The oxygen and carbon isotopic signatures of laminations in lacustrine stromatolites and palaeoenvironmental significances of growth rhythmites

作　　者：伊海生[1,2] 时志强[1] 惠博[1] 夏国清[1] 

机构地区：[1]成都理工大学沉积地质研究院,四川成都610059 [2]成都理工大学油气藏地质及开发工程国家重点实验室,四川成都610059

出　　处：《地学前缘》2009年第6期168-176,共9页Earth Science Frontiers

基　　金：国家自然科学基金项目(40972084;40572077);教育部博士点基金项目(20060616005)

摘　　要：青藏高原北部渐新统雅西措组湖相地层中的叠层石,具有典型的毫米级暗色富有机质纹层与浅色富碎屑纹层交替的生长节律,纹层形态呈穹窿状产出。为了探索湖湘叠层石纹层的成因和时间意义,我们采用激光微区采样技术分别对单个暗色纹层和浅色纹层进行了碳氧同位素分析。结果表明,每一个共轭纹层对中,暗色纹层相对于浅色纹层明显富集δ18O和δ13C,而且δ18O和δ13C之间具有正向变化关系,即δ18O和δ13C显示同步亏损和富集,反映季节性气候变化是影响纹层同位素信号周期性波动的主要因素,支持叠层石的对偶纹层为年纹层成因,它可以为气候和环境变化研究提供一种高分辨率地质材料。The lacustrine stromatolites from the Oligocene Yaxicuo Formation of the northern Tibetan Plateau display regular growth rhythms of dark（organic-rich layer）and light（sediment-rich layer）lamination alternations with millimeter scale.The lamination morphologies exhibit dome and columnar shapes in a vertical section.In order to understand the origin and time length scale of a couplet of laminae in stromatolites,the stable oxygen and carbon isotopic compositions of individual lamina were analyzed by using laser micro-sampling technique.The analysis results showed that the dark lamina in stromatolites commonly has relatively higher δ18O and δ13C values than the light lamina.The δ18O and δ13C values display positive covariance,i.e.,simultaneous enrichment in dark laminae and coeval depletion in light laminae.We believe that the cyclic fluctuations of isotopic signals among couplets of laminae were caused by seasonal climatic variations.We suggest that the couplets of laminae in lacustrine stromatolites indicate the origin of annual lamination.This study demonstrates the lamination in lacustrine stromatolites can provide us a kind of geologic material with high-resolution to reconstruct terrestrial palaeoclimate and palaeoenvironment changes during the geologic history.

关 键 词：叠层石 碳氧同位素 纹层成因 季节变化 湖泊环境 青藏高原 

分 类 号：P597[天文地球—地球化学]